1. Field
The disclosure relates to a hydrostatic mechanical transmission, and more particularly, to an efficient and optimal hydrostatic mechanical transmission equipped with an automatic manual transmission (AMT) type sub-gearshift which includes a hydrostatic transmission, a complex planetary gear, and an automatic manual sub-gearshift, facilitates spindle machining, and reduces material cost thereof.
2. Description of the Related Art
A hydraulic transmission system is commonly used in large vehicles or stationary equipment. However, the hydraulic transmission efficiency decreases as the output speed increases at a predetermined gear setting state. Accordingly, it is not an efficient way to perform a hydraulic transmission at the upper part of the gear setting. These problems may be solved by using multiple gear settings, but the advantage of the hydraulic transmission is degraded due to the complexity of the transmission.
As an alternative of the hydraulic transmission system, there is a mechanical transmission system. However, the existing mechanical transmission system is limited to a non-continuous gear ratio which does not permit the limitless speed ratio that is proved in a hydraulic transmission. In the full-speed output, there is a need to perform multiple types of power management between the engine and the transmission in order to maintain the efficiency of the transmission. The simple mechanical transmission is not appropriate for guaranteeing the efficient use of the effective power of the engine due to a non-continuous speed ratio. The simple hydraulic transmission has poor efficiency originally at a high operation speed.
Accordingly, there has been an attempt to provide the more efficient transmission system for large and small vehicles and stationary equipment by the combination of the hydraulic transmission system and the mechanical transmission system. Such a hydro-mechanical transmission system uses a hydrostatic mechanical structure in which the angle of the inclination plate of the variable displacement hydraulic pump is changed by a pedal operation, the operation speed of the fixed displacement hydraulic motor is changed to an endless stage, and the speed-change output is changed in multiple stages in a gear type transmission so as to drive a vehicle wheel.
As such a hydrostatic mechanical transmission system, a power distributing transmission is a multi-path transmission in which two or more power transmission paths are provided through a planetary gear, and is an endless transmission in which the entire transmission becomes an endless type by using the endless transmission as a variator in one path among the paths. Furthermore, the hydro-mechanical transmission (HMT) is a power distributing transmission which uses a hydrostatic transmission as a variator, and may be classified into a simple planetary gear type using one planetary gear and a complex planetary gear type using two or more planetary gears. In the planetary gear type, a sub-gearshift is disposed in rear of the planetary gear so as to have a plurality of speed ranges. And, the automatic manual transmission (AMT) is an automatic transmission obtained by automating a manual transmission, and in general, includes a synchro-type transmission gear, an actuator, and a power interrupting clutch.
Most of the sub-gearshifts of the hydro-mechanical transmissions adopt a wet multi-clutch type, and in order to improve durability and obtain soft intermitting performance of the clutch, the wet type is desirable, but slight power loss occurs due to the accompanying oil. Furthermore, as the configuration of the hydraulic system, spindle machining is not easy, a necessary space is wide, and high material cost is demanded.
Accordingly, there has been an attempt to realize the more efficient driving system for large and small vehicles such as a tractor, an automobile, and heavy equipment and stationary equipment by adopting a cheap automatic manual transmission (AMT) type instead of an expensive wet multi-clutch of a hydrostatic endless transmission type so as to reduce material cost and facilitate spindle machining.